rapid optical/x-ray timing of black hole binaries: correlated and non-linear...

Rapid Optical/X-ray timing of black hole binaries:

correlated and non-linear variability

Poshak Gandhi

(RIKEN, JSPS Research Fellow)‏

V. Dhillon, T.R. Marsh, A.C. Fabian (UK)‏K. Makishima, A. Kubota (Japan)‏

M. Durant, T. Shahbaz (Spain)‏J.M. Miller (USA)‏

H.C. Spruit (Germany)

Optical variability : Reprocessing of high energy photons

Optical power of X-ray binaries

Some sources show rapid direct optical variability

(Suleimanov+03)

GX 339-4 ESO PR 2008Artist: L. Calçada

Optical timingEarly indications:

but not followed up, nor fully understood‏

(GX

33

9-4

: M

otc

het a

l. 1

982)

sky

comparison

0.5s

Optical timingV4641 Sgr:

(Uemura et al. 2002)

XTE J1118+480

(Kanbach et al. 2001, Spruit et al. 2002)

Average X-ray flares

Average optical aroundX-ray flares

XTE J1118+480

(Kanbach et al. 2001)‏

Our observations

+

VLT RXTE

1. GX 339-42. Swift J1753.5-0127

ULTRACAM:ultra-fast, triple-beam CCD camera

Light-weight camera (visitor instrument on WHT/VLT/NTT)‏

Frame-transfer CCDs withnegligible dark current, dead-time

Speeds ~ 500 frames / sec

3 simultaneous optical filters

Absolute timing ~ 1 ms

http://www.shef.ac.uk/physics/people/vdhillon/ultracam/

ug

r / i / z

Observations

GX 339-4 Comparison

50 ms ULTRACAM frame (r' band)‏

PowerSpectrashow

broad-band noise

Op

tical

X-ra

y

Lorentziandecomposition

X-O Cross Correlation Function (CCF)‏A

vera

ge

Optical Lag (seconds) (Gandhi+ 2008)

Rapid variability origin?:

Simple reprocessing models

1. Small time delayA

vera

ge

Optical Lag (seconds) (Gandhi+ 2008)

150 ms

2. Anti-correlationA

vera

ge

Optical Lag (seconds) (Gandhi+ 2008)

150 ms

3. Small optical coherence times

X-rays

Optical

Optical ACFnarrower than X-ray ACF

Lag (s)

Au

to C

orr

ela

tio

n F

un

cti

on

(Po

isso

n c

orr

ecte

d)

3. Small optical coherence times

X-rays

Optical

Auto correlation functions

(rms2 normalization: Belloni+90)

Power spectra

GX 339-4: Simultaneous light curves

Swift J1753.5-0127: Simultaneous light curves

XTE J1118+480:Kanbach et al. 2001‏

GX 339-4:Gandhi et al . 2008

Swift J1753.5-0127:Durant et al. 2008

Complex optical/X-ray correlations

Non-linearvariability:

Random shotnoise predicts constant σ

(Gandhi 2009) Flux (f )

Va

ria

bility a

mplitu

de

(σ

)df f

dt

Additive shots ruled out

+

X

=

=

Superposition of independent shots =>

Ruled out in X-rays (Uttley et al. 2001…2005) and now optical (Gandhi 2009)

Flux

Non-linear variability

X =

Perturbations must be coupled together, rather than superposed

Interactions between multiple emission components(Lyubarskii 97, Misra 00, King+04, Titarchuk+07, Zhang 07)

X-ray binaries

(J. Orosz) Swift J1753.5-0127

XTE J1118+480

GX 339-4

V4641 Sgr

Summary

Simultaneous rapid optical/X-ray timing of X-ray binaries in low/hard state.

Optical not reprocessed.

Complex CCF => jet/corona/disk interaction

X-ray and optical r.m.s. scales with flux=> additive shots ruled out

Fast optical timing => interesting constraintson accretion and hot plasmas